Process for making nonwoven fabric of regenerated cellulosic fibers



Sept. 29, 1970 v, 55555 ET AL 3,531,344

PROCESS FOR MAKING NONWOVEN FABRIC OF REGENERATED CELLULOSIC FIBERS Filed Feb. 14, 1968 2 Sheets$heet l FIGJ INVENTORS EDWIN V. BEEBE JOHN A. LYNCH. JR.

ATTORNEY Sept. 29, 1970 E v. BEEBE E PROCESS FOR MAKIIIG NONWOVEN FABRIC OF REGENERATED CEILLULOSIC FIBERS Filed Feb. 14, 1968 2 Sheets-Sheet S FIG.2

RECENERATED CELLULOSIC FIBERS RANDOM DEPOSITION BATT -e- HYDRAULICALLY ENTANGLE BATT NITH ACTIVATED BONDING POINTS HEATING uouwoveu UNITARY FABRIC WASHING NET FABRIC DRYING SOFT FABRIC HAVING TENSILE STRENGTH OF I.O'4 LBS./IN.

SLIGHTLY 'SATURATING' DISCRETE AREAS WITH AOUEOUS CAUSTIC OF 6-I2% CONC.

TREAT ALTERNATE BANDS WITH CARBOXYNETHYLATING SOLUTION AND HEAT CARBOXYNETIIYLATED UNITARY FABRIC TREAT WITH AQUEOUS H2504 FABRIC HAVING BANDS OF CARBOXYIIETHYL CELLULOSE CONVERTING TO 'SODIUN SALT FORN.

JOHN A. LYNCH. JR.

ATTORNEY I United States Patent 3,531,344 PROCESS FOR MAKING NONWOVEN FABRIC 0F REGENERATED CELLULOSIC FIBERS Edwin V. Beebe, Newark, Del., and John A. Lynch, Jr.,

Chadds Ford, Pa., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Feb. 14, 1968, Ser. No. 705,404 Int. Cl. B32b 31/14 US. Cl. 156-83 7 Claims ABSTRACT OF THE DISCLOSURE Nonwoven fabrics of regenerated cellulose fibers are made by (a) treating a batt of the fibers With aqueous caustic in numerous small discrete areas, (b) heating the batt, (c) washing the fabric and drying.

Also a water-disposable nonwoven fabric is made by treating the batt after step (a) with an alkaline, celluloseetherifying reagent to form a grid of intersecting bands enclosing areas of untreated fibers, said areas having a maximum dimension of less than 2 inches, heating to bond the batt and etherify the grid, removing excess reagents and converting the cellulose ether portions to a highly swellable form.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to nonwoven fabrics made from cellulosic textile fibers without the use of twisting, weaving, knitting, sewing, or related processes. More specifically, it is concerned With soft nonwoven fabrics of regenerated cellulose fibers held together by self-bonding in discrete patterned areas.

The invention also encompasses the simultaneous selfbonding and carboxymethylation of the cellulosic fibers to yield a flushable fabric exhibiting adequate in-use integrity when wet with body fluids.

Description of prior art Nonwoven fabrics which obtain strength and integrity from discrete area bonding have become well-known in the art. One of the earlier patents in this field is Goldman, US. Pat. 2,039,312. Various improvements on the product have been made in subsequent patents, of which Drelich et al., US. Pat. 3,009,822 is typical. The self-bonding of regenerated cellulose fibers by a general application of aqueous caustic to the entire area of a nonwoven batt at room temperature or below has been described in several foreign patents. British Pat. 698,123 (complete specification published Oct. 7, 1953) seeks to obtain a surface action on the fibers and to control the destructive action of the caustic on the regenerated cellulose by rapidly diluting or neutralizing the alkali before the fibers are completely penetrated. The operation of this process tends to produce a stiff harshened fabric when sufiicient bonding is induced to give adequate coherence and tensile strength to the nonwoven Web. British Pat. 880,702 (complete specification published Oct. 25, 1961) attempts to overcome the tendency to fiber damage and harshening inherent in the low-temperature, total-fabric treatment by cross-linking the cellulose in the fibers before they contact the activating alkali hydroxide solution. British Pat. 880,703 (complete specification published Oct. 25, 1961) attempts to accomplish the same result by using a special spun-drawn high-crystallinity rayon fiber in the nonwoven web for caustic bonding. Both of these remedies require special, high-cost fibers as starting materials, which additionally may exhibit inherent brittleness and poor durability in the final product.

3,531,344 Patented Sept. 29, 1970 SUMMARY OF INVENTION It has now been discovered that, surprisingly, the disadvantages of the prior art processes can be overcome by applying the activating alkali hydroxide solution to only a small portion of the total fabric in discrete programmed areas and then bringing about interfiber bonding in these areas by drying the fabric at high temperature. Any conventional regenerated cellulose fiber may be used. The product shows, to an enhanced degree, the flexibility, softness, and fine hand of the point resin-bonded nonwoven fabric. The high-temperature drying appears to prevent the fiber destruction and em'brittlement which may accompany the use of high-swelling alkali hydroxide solutions on regenerated cellulose fibers at low temperatures.

The products of this invention are useful in all textile uses and are especially desirable where low cost is important and the utmost in hard-usage durability is not a primary consideration. Such uses include draperies, interliners, wiping cloths, disposable bed linens, and the like. The process is easily adapted ot the manufacture of lowcost single-use fabrics which can be disposed of by flushing away in an ordinary toilet.

The reusable products of this invention, being free of thermoplastic or solvent-soluble binders, can be pressed with a hot iron or dry cleaned in active solvents without fear of damaging the fabric or binder.

The invention in short is a process for making nonwoven fabric of regenerated cellulosic fibers which comprises:

(a) forming a batt of the fibers;

(b) treating from 15 to 40 percent of the batt surface in numerous small discrete ar as extending through the thickness of the batt with an aqueous 6 to 12 percent sodium hydroxide solution to activate inter-fiber bond ing points, the areas having a minor dimension of less than about 4; inch and being spaced apart by about to about A inch;

(c) heating the activated batt at a temperature within the range of about C. to C. to bond the batt into a unitary structure to form the fabric;

(d) washing the fabric to remove excess reagents; and

- then (e) drying the fabric, said dried fabric having a tensile strength of at least 1.0 lb./in. and a bending length of less than about 3 cm.

Also a process for preparing a biodegradable nonwoven fabric of regenerated cellulosic fibers having substantial strength when dried and upon exposure to body fluids, but that disintegrates into flushable pieces upon being subjected to a water stream in a toilet comprising: after step (b) treating discrete areas of the activated batt with an aqueous carboxymethylating solution containing from 5 to 30% sodium chloroacetate and from 2 to 10% of an alkali metal hydroxide, said treated area being in the form of a grid of intersecting bands enclosing areas of untreated fibers, said areas having a maximum dimension of less than about 2 inches; heating the batt at a temperature within the range of 100 to 150 C. to bond the batt into a unitary structure to form the fabric and to react the carboxymethylating solution with the cellulosic fibers, the carboxymethyl portions of the fabric having a degree of substitution within the range of about 0.20 to 0.50; treating the fabric with an aqueous bath containing a strong acid to convert the treated hands into carboxymethyl cellulose; treating the fabric with an aqueous alkaline solution to convert the carboxymethyl cellulose into the highly water-swellable sodium salt form, said solution containing a salt in sulficient concentration to prevent excess swelling of the sodium carboxymethyl cellulose;

3 and then drying the fabric. The batt may be lightly entangled prior to (b).

An alternate process uses a web consisting essentially of fibers aligned primarily in one direction. Following step (b) the etherifying solution is applied in the form of a plurality of discrete bands transverse to the direction of fiber alignment to form bands of untreated fibers having a width of less than about 0.5 inch and proceeding as above.

DESCRIPTION OF DRAWING In the accompanying drawing, FIG. 1 is a diagram of a machine on which the process of this invention may be carried out. The batt of fibers 1 from the card, Rando- Webber or other source, is first passed over the print roller 2 which presses the batt against resilient back-up roller 3 and imprints on the batt spots or lines of alkali solution in the desired pattern. Print roller 2 is supplied by transfer roller 4 with thickened alkali solution 5 contained in trough 6. Excess solution is scraped from print roller 2 by means of blade 7. Backup roller 3 may be advantageously covered with a polyethylene film to prevent it from becoming wet with the alkaline bonding agent. The imprinted batt is then placed on moving screen belt 8, driven and supported by rollers 9. The screen belt carries the imprinted batt through circulating hot-air oven which dries and bonds the fibers, and then under spray showers 11, 12, 13 which wash the alkali from the bonded nonwoven fabric. Shower 11 or shower 12 may be very dilute acid such as 1% acetic acid or 1% lactic acid to assist in removing the caustic from the cellulosic fibers. The washings are allowed to drain into boxes 14 and may then be run into a sewer or pumped to recovery facilities for reuse. The washed fabric is finally passed between squeeze rolls 15, dried on hot rolls 16, and wound up on collecting roll 17 FIG. 2 is a flow chart of the process of this invention that is based on the actual examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Suitable starting materials The fiber batts or webs that are to be self-bonded to coherent integral fabrics by the process of this invention must contain primarily regenerated cellulose fibers. The regenerated cellulose may be viscose rayon, cuprammonium rayon, or any other type of man-made cellulosic fiber. In most cases, a minor amount of other fibers which are less responsive to the alkaline activating liquid may be admixed with the regenerated cellulose fibers. Examples of such unresponsive fibers are cotton, nylon, and polyester fibers. Such fibers may, in some cases, be some- What weakened by the hot alkali during the drying step of the process of this invention. In addition, the presence of inert, unbonded fibers generally tends to decrease the overall tensile strength of the nonwoven fabric. Hence, the use of amounts of non-responsive fibers in excess of should be undertaken only with caution, depending on the tensile strength and abrasion resistance needed in the final product.

The usual starting material for nonwoven fabrics is a basic Web of staple-length fibers. The basic web has very little integrity or strength and the alignment of the fibers with one another may vary from complete randomness to complete unidirectionality. Such webs may be made by carding, air deposition, or liquid deposition of fibers. The fibers usually have an average length of 0.5 to 2.5 inches (1.27 to 6.35 cm.) in the carding and air deposition operations. Liquid deposition from water slurries usually requires fibers of 0.25 to 0.5 inch (0.635 to 1.27 cm.) staple length. Fibers up to 6 inches (15 cm.) may be used in some dry processes and continuous filaments may be used in a direct laydown process.

The single webs can be combined to form layers of different fiber alignments or different fiber lengths, such as a continuous filament web and a staple fiber web.

The use of the simple fibrous webs described results in the formation of nonwoven final fabrics which are strong and useful but lacking the appearance of conventional textile fabrics. In uses where it is desirable to have the appearance of conventional textile fabrics, the structure may be patterned or textured. In addition, the texturing operation may be carried on with sufficient intensity that the resulting fiber entanglement contributes to the surface integrity and over-all tensile strength of the fabric.

Simple patterning, without any substantial amount of entangling to enhance fabric integrity, may be done by subjecting the fibers in the basic web to a stream of fluid particles in a rearranging zone as taught by Kalwaites in US. Pat. 2,881,251 and 3,081,501 or by Gelpke in US. Pat. 3,137,893. A texture resembling that of a woven fabric coupled with a greater degree of fiber entanglement for fabric reinforcement may be accomplished by the method of Guerin in US. Pat. 3,214,819 or preferably the method of Belgian Pat. 673,199 (Evans). For reasons of economy, fibrous webs which are to be given integrity by self-bonding are only lightly entangled in this process, since fully entangled fabrics possess adequate strength and durability without additional bonding.

THE BONDING PROCESS The restraining bonds in nonwoven fabrics are often provided by the application of an adhesive. Alternatively, the surfaces of some or all of the fibers may be softened or activated by the application of heat, solvent or swelling agent so that the fibers tend to coalesce and adhere to each other after the activating influence is withdrawn or inactivated. When the adhesive or activating medium is applied uniformly over the entire web, a stiffening and harshening of the fabric generally results. The stiffening effect is largely avoided by confining the adhesive or bonding influence to relatively small discrete areas separated by areas of unbonded fiber elements. A restricted movement of fibers relative to each other may thus be achieved, coupled with a hinged effect between bonded areas. The result is a soft, strong, nonwoven fabric of pleasing quality.

By the expression discrete bonded areas is meant that at least 40% of the fabric consists of fiber exclusive of any bonded areas. The bonded areas may form an interconnecting network, but preferably take the form of separate spots or figures. The discrete spots or figures may be advantageously so shaped and arranged that no extended straight line can be drawn in any direction in the unbonded areas without encountering a bonded spot. Highly-oriented Webs such as may be prepared by carding may also be effectively bonded in lines running across the fibers. The lines may be straight, curved, or wavy and may be continuous or discontinuous. They may be about as wide as the clear width between lines but the lines are preferably about 1 to 3 mm. wide, separated by spaces about 2 to 5 mm. wide.

The maximum distance between bonded areas must be slightly less than the average length of fibers in the fabric. For preferred products, the distance. between bonded areas will be much less. Suitable patterns for bonded areas are discussed in US. Pats. 2,039,312; 2,- 705,687; 2,705,688; 3,009,822; and 3,120,449.

In the process of the present inventiomdilute aqueous alkali is applied to the nonwoven web in the discrete programmed areas where it is desired to bring about bonding. The alkaline solution may be sodium hydroxide of 6 to 12% concentration by weight, preferably of 6 to 8%. It may be used in its ordinary low viscosity form or it may contain a thickener to assist in its uniform application by high-speed mechanical means thereby avoiding substantial lateral wicking of the caustic to areas outside of the discrete area desired.

The unthickened alkaline solution may be applied to the web by means of an atomizing spray using a perforated plate to mask or protect those areas which are to remain in the unbonded condition. In those cases where the bonded areas take the form of elongated lines, as in the cross-bonding of oriented carded batts, the solution may be hand-applied with a hypodermic needle guided by a template.

Thickened solutions may be conveniently used in hand application through a fine screen such as is used in silk screen printing. The opaque parts of the screen protect those parts of the fiber web which are to remain unbonded. The thickened solution is most useful in highspeed commercial operation. The solution is most conveniently applied by means of letter-press print roller such as is described by Goldman in U.S. Pat. 2,039,312 or an engraved print roller as described by Hess in US. Pat. 2,705,686 and by Goldman in U.S. Pat. 2,545,952.

The thickener used in the alkaline activating solution should preferably be one which is effective at low concentration, so that a minimum amount of foreign solid material is used. The thickener should also be one which is compatible with both acid and alkaline solutions so that it will not be coagulated by an acidic neutralizer and remain on the nonwoven fabric. A particularly preferred thickener is a complex bacterial polysaccharide sold under the trade name Kelzan by Kelco Co. of Chicago, Ill. A concentration of 0.1 to 0.25% is usually sufficient. Other gums and resins for thickening aqueous solutions are well known in the art and readily available on the market.

The amount of alkaline activating solution to be added will depend on several factors. In most cases, the nonwoven web should be wet completely through to the side opposite the point of application. This will insure that all fibers passing through that segment of the web will become fastened in place. On the other hand, the amount of liquid used should not he so abundant as to encourage wicking laterally to areas outside the discrete programmed areas in which it is intended that bonding should occur. The thickened solutions used in the highspeed printing process help to suppress lateral wicking. The amount of solution needed to wet through the web locally will depend on such factors as weight and thickness of the fabric, filament denier of the fibers, and degree of fiber orientation, and the degree of entanglement (if any). An alternative way of bonding the fibers and minimizing lateral wicking is to apply less solution than is needed to completely penetrate the fiber batt, on both sides in a staggered pattern as taught in U.S. Pat. 3,120,449.

Following the application of the alkaline activating fluid, bonding is brought to completion by drying the fabric with heat. Although the timing of this operation is not critical, it is desirable to complete the process as rapidly as possible for economic reasons. The imprinted fabric should not be allowed to stand until drying at room temperature takes place, or canbonation of the caustic by atmospheric carbon dioxide occurs. For piece-work operation drying may be carried out on a hot plate, in an oven, or on hot rolls. In the preferred continuous operation drying and the resulting bonding is effected by passing the impregnated wet fabric through a hot-air oven. Dielectric or infra-red radiant heating may be employed.

Drying and bonding may be carried out at any temperature between 100 and 150 C. or even higher. In general, the preferred temperature is from 115130 C. This temperature range gives reasonably rapid drying for continuous operation, with a minimum of harmful effects to the fabric. The process of heating to complete the bonding leaves the fibers in the bonded areas intact but firmly adhered together without any stiffening effect from added resinous binder. Although we do not wish to be bound by any particular theory or mechanism of reaction,

it is postulated that a favorable type of bonding takes place during the heating process, since the swelling of regenerated cellulose in aqueous alkali is well known to decrease as the temperature rises. The deswelling effect is then further accentuated as moisture is evaporated.

The drying time required will depend strongly on the fabric being used. It will also depend on the speed of circulation of the surrounding atmosphere. A light-weight fabric, of 1 oz./yd. or less, may be dried in an oven at C. with rapid air circulation in 15 seconds or less. Up to one minute may be required on a hot plate or hot roll not provided with forced air circulation. Thicker fabrics, containing larger amounts of liquid, will take correspondingly longer to dry.

When it is desired to prepare a fiushable fabric by the process of this invention, it is advantageous to superimpose on the wet caustic-printed batt, a printed pattern of a reagent which will convert the affected fibers to a water-sensitive derivative during the same baking treatment which completes the caustic-bonding process. One such reagent printing pattern forms a grid of interconnecting lines surrounding a plurality of discrete areas of essentially unmodified, caustic-point-bonded regenerated cellulose fibers with a maximum dimension of less than 2 inches (5 cm.) each. Preferably, the discrete areas (non-water sensitive) are in the form of squares or hexagons about /2 inch (1.3 cm.) across. The final fabrics are particularly useful in the construction of flushablc diapers.

Another modifying reagent printing pattern consists of straight or wavy lines running between lines of caustic bonding solution printed across the direction of orientation of the fibers in a carded batt. The final fabric in this case will have its principal strength in the direction of fiber orientation and will be particularly useful as a loadbearing cover fabric in the construction of flushable sanitary napkins.

The modifying reagent used should be one which converts the regenerated cellulose into an ether or ester derivative which is soluble or very weak in ordinary water but which maintains adequate strength in use when wet with salt-containing body fluids. Polyelectrolytes are particularly susceptible to deswelling by such salt solutions. A preferred cellulose derivative for the present purpose is, accordingly, the sodium salt of the carboxymethyl ether of cellulose having a degree of substitution of 0.2 to 0.6, and preferably of 0.3 to 0.5 ether groups per glucose unit. Other derivatives of cellulose such as the carboxyethyl ether, or the partial (acid) esters of polybasic acids such as phthalic acid, succinic acid, sulfuric acid, or phosphoric acid have been found suitable for use in water-flushable fabrics with adequate strength in use.

The preferred reagent for use in making the watersensitive salt of the carboxymethyl ether of regenerated cellulose is a freshly-prepared water solution containing 10 to 30% sodium chloroacetate and 2 to 10% of sodium hydroxide. A typical reagent contains 20% sodium chloroacetate and 4% sodium hydroxide, with 0.5% of high viscosity commercial sodium CMC added as a thickener. The alternating lines of bonding caustic and etherifying reagent may typically be about inch (1.6 mm.) wide, separated by about 4; inch (3.2 mm.) of dry fibers.

The etherification reaction with alkaline sodium chloroacetate is brought to completion at the same time and under the same conditions are are used to complete the caustic bonding. The reaction is carried out at tempera tures of 110 to C. for times varying from 10 seconds to 10 minutes. It may be necessary to extend, slightly, the time needed for caustic bonding alone, when carboxymethylation is being carried out simultaneously. Very considerable savings in operating costs and in investment in equipment may be realized by using one heating process to simultaneously self-bond and chemically-modify to a water-sensitive form different intermingled portions of a rayon fiber batt to produce a fiushable nonwoven fabric.

Final treatments of bonded fabrics After the heating and drying of the caustic-programmed-area-bonded rayon nonwoven fabric is completed, it is then necessary to remove the alkali from the fabric for most purposes. This can be done by simple washing with water in any known manner, for example, by passing under a series of showers or through a series of dip-tanks with counter-current water fiow. As is well known, alkali is very difficult to remove completely from rayon by washing alone. For this reason it may be desirable to neutralize the caustic in a dilute acid bath, either immediately after heating or after a preliminary rinse to remove the bulk of the alakli. 'In either case the acid neutralizer is washed out and the final fabric is dried on heated rolls, or by any other drying means.

When the fabric has been simultaneously causticbonded and chemically modified to give a flushable fabric a somewhat different procedure is followed. The carboxymethyl cellulose areas produced in the preferred process are extremely weak or actually dissolve in dilute solution of sodium hydroxide. Hence, rinsing out free alkali with plain water may lead to destruction or damage to the fabric. In this case, the heated and dried fabric is first treated with a dilute solution of a strong mineral acid such as sulfuric acid. This converts the carboxymethyl cellulose to the free-acid form which is relatively low-swelling and therefore the fabric retains its strength substantially in plain water. When relatively high degrees of carboxymethyl substitution are used it may be desirable to include a deswelling salt in the initial acid bath or shower, for example 5% sulfuric acid containing 15% sodium sulfate. See Mann, US. Pat. 3,328,892 dated July 4, 1967, for suitable deswelling salts. In either case, any remaining reagents, by-products or other impurities may now be washed out with water. The carboxymethyl cellulose areas are then restored to the high-swelling sodium salt form by treating the entire fabric with a slightly alkaline buffer in a strongly deswelling salt solution, preferably at a pH of 8 to 9. A preferred solution for this purpose contains 2% disodium phosphate and 4% to 8% sodium sulfate, adjusted to a pH of 8.5. After treatment in such a bath, the fabric is passed through squeeze rolls or other dewatering device to remove as much salt solution as possible. The fabric is then dried with mechanical working to help soften the fabric and remove as much free crystalline salt as possible. The final prodnot is a soft, pleasant, flushable fabric in which both the chemically modified areas and the bonded areas are essentially invisible until the fabric is wet.

Testing procedures Samples used for tensile tests, and measurement of fabric weight are conditioned at 70 F. (21 C.) and 65% relative humidity for at least 24 hours before testing under these conditions.

Tensile strengths and elongations are measured on 1.0 X 2 inch (2.54 X 5.08 cm.) samples at an elongation of 50% per minute on an Instron testing machine. The results are in pounds/inch (grams/centimeter), herein designated as lbs/in. (g./cm.). Samples are soaked for 5 minutes in distilled water at 21 C., or other test liquid where specified, and then clamped in the tester and broken in air to determine wet strip-tensile strength.

Fabric weights are determined by dividing the weight of a fabric sample by its area and are expressed in ounces/sq. yard (grams/square meter) herein designated as oz./yd. (g./m.

Bending length is a measure of the softness and drape of a fabric and is defined as half the length of a strip of sample that bends under its own weight to a 45 angle. It is determined on a 1 x 6 inch (2.54 x 15.2 cm.) sample on a Drape-Flex Stiffness Tester (made by Fabric Development Tests, Brooklyn 32, N.Y.). The procedure of A.S.T.M. Standard Method D'1388-55T is followed.

All properties measured in synthetic urine are determined using a salt solution similar in composition to human urine. It is made up of 10 g. of NaCl, 24 g. of urea, 0.6 g. of MgSO 0.7 g. of calcium acetate monohydrate, and 964.7 g. of distilled water. A solution termed synthetic hard water containing 0.4 g. of calcium acetate monohydrate, 0.175 g. of MgSO and 999.4 g. of distilled water is used in determining properties in hard water.

In the examples, all reagent percents refer to weight percent unless otherwise specified.

EXAMPLE I Rayon fibers of 1.56 inches (3.94 cm.) length and 1.5 denier per filament are made into a batt of randomly oriented fibers by an air deposition process using a Rando- Webber machine (made by Curlator Corp. of East Rochester, N.Y.). The batt has an average weight of 1.0 oz./yd. (33.9 g./m. A portion of this batt is sandwiched between two thin metal plates containing a rectangular array of inch (1.2 mm.) diameter holes whose centers are A; inch (3.2 mm.) apart in both principal directions. The plates are so arranged that the holes are opposite each other. The holes expose 19.5% of the fabric surface area. A 6% solution of sodium hydroxide in water is sprayed from an atomizer against the sandwich from both sides so that the fibers visible through the holes are lightly but thoroughly moistened to substantial saturation with the 6% NaOH solution. The batts, still between the perforated plates, are then dried for 4 minutes in an oven at C. The resulting nonwoven fabric is washed free of caustic in running tap water, squeezed out, and dried in air.

The same process is repeated with other portions of the rayon batt but solutions containing 4% and 8% NaOH are sprayed through the holes in the metal plates. The final dried fabrics are tested for dry tensile strength with the results as folows.

Concentration of NaOH Breaking (percent) strength 4 0.06 lb./in. (l1 g./cm.)

6 2.8 lbs/in. (500 g./cm.)

s 3.0- lbs/in. (535 g./cm.)

EXAMPLE II Rayon fibers of 1.56 inches (3.94 cm.) length and 1.5 denier per filament are made into a batt of randomly oriented fibers by an air deposition process using a Rando- Webber machine. The batt has an average weight of 1.0 oz./yd. (33.9 g./m. A thickened activating solution is prepared containing 12% NaOH and 0.25% of Kelzan as a thickening agent. The solution is applied to the rayon batt by using a rubber blade to force the solution through the clear portions of a Dacron screen such as is used in silk screen printing. The screen is originally covered with impermeable material which has been altered to contain a rectilinear array of inch (2.4 mm.) diameter clear round areas whose centers are A inch (6.35 mm.) apart. The corresponding areas of the rayon fiber batt are thus moistened with the thickened 12% NaOH solution. About 22% of the total fabric area is thus treated with the activating liquid. The fabric is then dried for 4 minutes on a hot plate at 120 C., washed free of caustic and thickener in tap water, and then dried in air.

The process is repeated using a different printing screen in which the circular clear areas are inch (1.2 mm.) in diameter with their centers /3 inch (3.2 mm.) apart causing 22% of the fabric area to be treated. The alkaline solution applied amounts to 3.2 g./ g. of fiber in the moistened areas. The final bonded nonwoven fabrics have Drapeflex,

crn. Breaking strength 1. 36 2.0lbs./in. (357 g./e1n.). 1. 57 3.8 lbs/in. (680 g./cm.).

Bonding pattern 932 x inch (2.4 x 6.35 mm.) 364 x inch (1.2 x 3.2 mm.)

EXAMPLE III This example illustrates the conversion of the bonded web to a fiushable form simultaneously with the formation of the inter-fiber bonds.

Rayon fibers of 1.56 inch (3.94 cm.) length and 1.5 denier per filament are made into a batt of randomly oriented fibers by an air deposition process using a Rando- Webber machine. The batt has an average weight of 1.0 oz./yd. (33.9 g./m.

The rayon batt is first marked off with narrow lines of 8% NaOH activating solution, using a #26 hypodermic needle guided by a template to locate the lines inch (6.35 mm.) apart. A second set of lines of activating solution, again inch (6.35 mm.) apart is supplied at a 90 angle with the first set, producing a grid of inch (6.35 mm.) squares.

About 35% of the fabric area is thus activated for bonding with grid lines of about inch in width.

The reagent for chemical modification of the fabric is made up to contain 20% of monochloroacetic acid, 4% sodium hydroxide, and 0.5% of Kelzan thickener. This is applied to the rayon batt previously lined with binder caustic, by means of a fine Dacron screen such as is used in silk screen printing. The screen is originally covered with impermeable opaque material which is then altered to contain a grid of 0.625 inch (1.59 cm.) squares of opaque coating separated in both directions by straight clear lines 0.125 inch (0.32 cm.) wide. The opaque sections keep the reagent from contacting the fibers whereas the reagent flows through the open lines to the fibers. The silk screen is placed in contact with the caustic-patterned batt and the thickened chloroacetate reagent is forced through the screen with a rubber blade until the batt has picked up about 180% of its original grid of caustic binder solution. The grid of chemical modifier solution and the caustic bonding solution are dried by heating the treated batt on a hot plate at 120 C. for 4 minutes. The dried fabric is acidified in a solution containing 5% sulfuric acid and 15% sodium sulfate, squeezed out, and neutralized in a solution containing 3% disodium phosphate and 17% sodium sulfate adjusted to a pH of 8.5. The final fabric is pressed be tween blotters and dried in a home laundry dryer at 40 C.,'while tumbling with a baseball 9.7 cm. in diameter. The final fabric has the appearance of a soft felt with good cover and aesthetic appeal. The dry tensile strength is 1.7 lbs/in. (304 g./cm.). In synthetic urine the tensile strength is 0.04 lb./in. (7.2 g./cm.) but in hard water the strength is only 0.014 lb./in. (2.5 g./cm.). The fabric easily breaks up into individual /3 inch (1.59 cm.) squares in quietly swirling water of very mild turbulence. Since there is no added resinous binder present, the entire structure is readily biodegradable in any sewage disposal system.

EXAMPLE IV This example makes use of a patterned and partially entangled batt to yield a bonded product of textile-like appearance and improved surface stability.

Rayon fibers of 1.56 inch (3.94 cm.) length and 1.5 denier per filament are made into a batt of randomly oriented fibers by an air deposition process using a Rando- Webber machine. The batt has an average weight of 1.0 oz./yd. (33.9 g./m.

The fibers of the batt are first entangled by supporting it on a wire screen and passing it under a row of vertical columnar jets of water as described in Belgian Pat.

673,199. In this case the supporting screen is a plain woven wire screen containing 18 wires per inch (2.54 cm.) in one direction and 20 wires per inch (2.54 cm.) in the other, with about 24% open area. The fabric and screen are passed twice at 12 ft./min. (3.66 m./min.) under a row of 40 jets per inch (2.54 cm.) of 0.005 inch (0.127 mm.) diameter, supplied with water at lbs/in. (7.0 kg./cm. pressure. The fabric assumes the appearance of a plain woven fabric.

The lightly entangled fiber fabric is subjected to selfbonding using 8% NaOH in the general method described in Example I. In this case, the holes in the thin metal plates are off-set rectangular openings set at right angles so that each end of each hole points toward the center of the side of another opening. The openings represent about 32% of the total area, and are approximately 3 mm. x 6 mm. The ends of the openings are slightly convex, and the sides are slightly concave. The patterned, entangled fabric before bonding has a dry tensile strength of 0.16 lb./in. '(29 g./cm.). The final bonded product has a tensile strength of 1.8 lbs/in. (322 g./cm.).

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

What is claimed is:

1. A process for making nonwoven fabric of regenerated cellulosic fibers which comprises:

(a) forming a batt of the fibers;

(b) treating from 15 to 40 percent of the batt surface in numerous small discrete areas extending through the thickness of the batt with an aqueous 6 to 12 percent sodium hydroxide solution to activate interfiber bonding points, the areas having a minor dimension of less than about inch and being spaced apart by about to about 4 inch;

(c) heating the activated batt at a temperature within the range of about 100 C. to C. to bond the batt into a unitary structure to form the fabric;

(d) washing the fabric to remove excess reagents; and

then

(e) drying the fabric, said dried fabric having a tensile strength of at least about 1.0 lb./in. and a bending length of less than about 3 cm.

2. The process as in claim 1 wherein the fibers are rayon staple of 1 to 2 denier per filament having a length of 1 to 2 inches and the batt has a basis weight of about 1 ounce per square yard.

3. The process as in claim 1 wherein the batt is hydraulically entangled to a tensile strength of at least 0.15 lb./ in. between steps (a) and (b).

4. A process for preparing a biodegradable nonwoven fabric of regenerated cellulosic fibers having substantial strength when dried and upon exposure to body fluids, but that disintegrates into fiushable pieces upon being subjected to a water stream in a toilet comprising:

(a) forming a batt of the fibers;

(b) treating from 30 to 40 percent of the batt surface in numerous small discrete areas extending through the thickness of the batt with an aqueous 6 to 10 percent sodium hydroxide solution to activate interfiber bonding points, the areas having a minor dimension of less than about inch and being spaced apart by about A to ,4 inch;

(c) treating discrete areas of the activated batt with an aqueous carboxymethylating solution containing from 5 to 30% sodium chloroacetate and from 2 to 10% of an alkali metal hydroxide, said treated area being in the form of a plurality of bands alternating with bands of untreated fabric extending in at least one direction, each treated band having a width of less than about 0.5 inch;

((1) heating the batt at a temperature within the range of 100 to 150 C. to bond the batt into a unitary 11 structure to form the fabric and to react the carboxymethylating solution with the cellulosic fibers, the carboxymethyl portions of the fabric having a degree of substitution within the range of about 0.20 to 0.50;

(e) treating the fabric with an aqueous bath containing a strong acid to convert the treated bands of (0) into carboxymethyl cellulose;

(f) treating the fabric with an aqueous alkaline solution to convert the carboxymethyl cellulose into the highly water-swellable sodium salt form, said solution containing a salt in sufiieient concentration to prevent excess swelling of the sodium carboxymethyl cellulose; and then (g) drying the fabric.

5. The process as in claim 4 wherein in step (a) the fibers are aligned primarily in one direction and in step (c) the carboxymethylating solution is applied in discrete bands transverse to the direction of fiber alignment alternating with bands of untreated fabric with each having a width less than about 0.5 inch.

6. The process as in claim 4 wherein in step (a) said batt is formed by random deposition and in step (c) the carboxymethylating solution is applied in thin bands extending in at least two directions forming a grid pattern defining a plurality of discrete untreated areas surrounded by treated areas, said untreated areas having a maximum dimension of less than about 2 inches.

7. The process as in claim 4 wherein the fibers are rayon staple of 1 to 2 denier per filament having a length of 1 to 2 inches and the batt has a basis weight of about 1 ounce per square yard.

References Cited UNITED STATES PATENTS 1,989,100 1/1935 Lilienfeld 8125 2,447,914 8/ 1948 Ruperti 8125 XR 2,486,803 11/1949 Seymour et al. 117143 XR 2,497,519 2/1950 Stevenson et al 8l25 3,009,822 11/1961 Drelich et al. 117140 XR BENJAMIN R. PADGETT, Primary Examiner S. HELLMAN, Assistant Examiner US. Cl. X.R. 

